Mono vs. multi How many MPPT channels are good for my project?€¦ · February 19, 2020 Slide 5 MPPT –a real key inverter attribute Comparing multi-MPPT vs single MPPT (single

—

February 19, 2020 Slide 1

—PRODUCT MANAGEMENT, REV. FEBRUARY 12- 2020

Mono vs. multi – How many MPPT channels are good for my project?PV Magazine webinarAndrea Genovesi, Marco Trova

—


Multi – MPPT: does it really matter?

Behind the technicality of MPPT - a real key inverter attribute

Promoting decentralized “combiner-free” PV system design

Enabling efficient PV system design and maintaining maximum yield under any scenario

Lowering LCOE through Opex and Energy Yield optimization: fuseless design/ integrated diagnosis

What are the tangible advantages of multi-MPPT in the design and over the lifecycle of a PV system?

—


MPPT = Maximum Power Point Tracking

MPPT – a real key inverter attribute

PDC = ηMPPT ٠PMPP

PDC

PMPP

PDC

VDCVMPPV

P

MPP-Tracker

Irr Pmpp

T

f(Irr,T)

?

I-V & P-V Curve

0.2

0.4

0.6

0.8

1.0

I/In

Cu

rre

nt

[p.u

.]

60

120

180

240

300

Po

we

r[W

]

360

0

Voltage [V]5 10 15 20 25 30 35 40 450

MPPT ?

HOW GOOD ARE YOUR REAL TIME MPP TRACKING

PERFORMANCEUNDER IDEAL

PV ARRAY CONDITIONS ?

Voltage

Po

we

r

0 Voc

Global Pmax

Local Pmax

Vmin

INITIALIZINGSCANNINGTRACKING

EFFECTIVE MPP SCAN REQUIRES WIDE MPP VOLTAGE RANGE!

HOW GOOD IS YOUR MPP TRACKING IN MINIMIZING SHADING LOSSES?

ηMPPT Ranking

< 99.0 Poor

> 99.5 OK

> 99.8 Excellent

—



MPPT tracking in single-MPPT monolithic inverter design: additional mismatch losses

Shading

PMPP = f(G, T)

Grid-connected PV- Inverter

PAC = η · PDC

PAC = ηTOT

· PMPP

PDC = ηMPPT

· PMPP

PDC

PAC

T

G

Temperature

Ohmic

Mismatch

Low Irradiance

SoilingShading

Temperature

Soiling (& snow)

Array electrical mismatch lossesinduced on monolithic MPPT by:

—



Comparing multi-MPPT vs single MPPT (single stage) inverter design: key benefits

0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0D

C P

ow

er

[p.u

.]

DC Voltage [V]

0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0

MPPT P-V Capability curves: 1500Vdc Inverters

Multi-MPPT DOUBLE STAGE INVERTER

KEY BENEFITS

❑ Wide input voltage range, extendedtowards lower MPP voltage values

❑ Ability to always track the MPP point, alsoin case of shaded strings

❑ Support complex PV field configurationsminimizing yield losses

❑ Practically immune to electrical mismatchlosses induced by shading, snow, soiling

❑ MPP voltage range not depending on AC voltage (decoupling of DC & AC voltagelevels)

SINGLE MPPT / SINGLE STAGE CONVERTER

MPP

INVERTER

PV1 PVn600V

MULTI-MPPT DOUBLE STAGE CONVERTER

MPP1

MPPn

PV1

PVn

INVERTER

Up to 800V

—



Multi-MPPT vs single MPPT (single stage) inverter design: behavior with partially shaded arrays

0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0

Portrait Landscape

1 2 25 26 27 28 1 2 26 27 28

DC

Po

wer

[p.u

.]

DC Voltage [V]

Shaded Area

30% of the modules are partially shaded(9 out of 28 in series)

100% of the modules are partially shaded(less than 30% of the surface)

PV curveUnshaded & partially shaded string

unshaded string

partially shaded string

—





MPP1

MPPn

PV1

PVn

INVERTER

Up to 800V

0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0

DC

Po

wer

[p.u

.]

DC Voltage [V]

PV curvepartially shaded string

double stage inverter


absolute maxima Vmpp within the input capability of the inverter

1 2 25 26 27 28 1 2 26 27 28

Shaded Area

30% of the modules are shaded(9 out of 28 in series)

100% of the modules are shaded(less than 30% of the surface)

Always tracking absolute MPP under anycondition, including partially shaded arrays

—



MPP

INVERTER

PV1 PVn600V



0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0

DC

Po

wer

[p.u

.]

DC Voltage [V]

PV curvepartially shaded string

single stage inverter

partially shaded string1 2 25 26 27 28 1 2 26 27 28

Shaded Area

30% of the modules are shaded(9 out of 28 in series)

100% of the modules are shaded(less than 30% of the surface)

Yield losses of single MPPT / single stage inverterswhen operating with partially shaded arrays

Absolute maxima Vmpp belowthe input capability of the inverter

Power loss due to narrowinput range

—



MPP

INVERTER

PV1 PVn600V



0 200 400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1.0

DC

Po

wer

[p.u

.]

DC Voltage [V]

PV curveUnshaded & partially shaded string

single stage inverter

unshaded string


1 2 26 27 28

Shaded Area100% of the modules are shaded

(less than 30% of the surface)

Power losses due to voltage mismatchinduced by shadingwhen paralleling shaded& unshaded strings on a single MPPT

Yield losses of single MPPT / single stage inverterswhen operating with partially shaded arrays

1 2 26 27 28

Unshaded string

—


Mono vs. Multi – MPPT


Using commercial software we have simulated several possible scenarios using single or Multi-MPPT inverters to evaluate the impact on the Yield

❑ Fixed Tilted Ground Mounted or Rooftop system

❑ Portrait or Landscape architecture

❑ Several shadow conditions analyzed

❑ South or East/West oriented systems

❑ Different Locations (Low Irradiance / High Irradiance)

The simulations were performed with PV*SOL premium

—




Array configuration: 3-high landscape

21/12 @ 12:00 21/12 @ 12:00 21/12 @ 13:00

Location North Europe

Tilt 20°

DC/AC ratio 1,3

GHI [kWh/m2] 1006.13

Low Irradiance Scenario

2,8m3,9m 1,9m

1 2 26 27 28

MPPT 2

MPPT 1

MPPT 3

MPPT

Multi MPPT

Single MPPT1 2 26 27 28

—


1 2



Multi MPPT Single MPPT

21/12 @ 12:00

+1,4%

+6%

<0,1%

21/12 @ 12:00

2,05m1,75m

Single MPPTMulti MPPT Single MPPT

2,05m1,75m

Location Middle East

Tilt 20°

DC/AC ratio 1,3

GHI [kWh/m2] 1831.89

Array configuration: 3-high landscape

1 2 26 27 28

MPPT 2

MPPT 1

MPPT 3

MPPT

Multi MPPT

Single MPPT1 2 26 27 28

High Irradiance Scenario

—


0,00%

1,00%

2,00%

3,00%

4,00%

5,00%

6,00%

1 2




5,3m

1 2 25 26 27 28

Unshaded string

0,00%

1,00%

2,00%

3,00%

4,00%

5,00%

6,00%

1 2 21/12 @ 12:00Multi MPPT Single MPPT

2,8m

1 2 25 26 27 28

Shaded string

Low Irradiance ScenarioMulti MPPT

Single MPPT

1 2 25 26 27 28

MPPT 1

MPPT 2

MPPT

1 2 25 26 27 28

21/12 @ 12:00

Array configuration: 2-high portrait


Tilt 20°

DC/AC ratio 1,3

GHI [kWh/m2] 1006.13

—




0,00%

0,50%

1,00%

1,50%

2,00%

1 2

0,00%

0,50%

1,00%

1,50%

2,00%

1 2Multi MPPT Single MPPT


Tilt 20°

DC/AC ratio 1,3

GHI [kWh/m2] 1006.13


Tilt 10°

DC/AC ratio 1,3

GHI [kWh/m2] 1006.13

3-high landscape / Tilt 10°

2-high landscape /Tilt 20°


Mult i MPPT

MPPT1

MPPT2

MPPT3

MPPT4

EAST

WEST

Single MPPT

MPPTEAST

WEST

Mult i MPPT

Single MPPT

MPPT

MPPT1

MPPT2

MPPT3

MPPT4

MPPT5

MPPT6

WEST

EAST

WEST

EAST

10°

20°

—


Mono or Multi – MPPT ?

How many MPPT channels are good for my project?

MONO MULTIIDEAL CONDITIONS!

❑ String length is not an issue and can be optimized to match the narrow MPP voltagewindow (OK for climates with limitedtemperature excursions)

❑ Land is flat or with very limited ripple

❑ Modules are mounted in portrait

❑ Land coverage ratio is not critical(unconstrained space / low cost of land lease)

?

❑ Best choice with landscape PV modulemounting layout

❑ Best choice when maximum land coverageratio shall be achieved

❑ Best choice when land planarity is notguaranteed

❑ Minimize the yield losses caused by electricalmismatch between different strings (shadingor different orientation)

BUT WHAT OTHER FACTORS SHALL BE CONSIDERED UNDER REAL WORLD CONDITIONS?

—


Mono or Multi – MPPT ?

How many MPPT channels are good for my project?

Soiling effects on performance

Especially at low tilt angles, soiling is building up mostly on the lower frame rail of the modules.This layer of dirt is shadowing the underlying cells, resulting in hot-spots and significant yield losses that are more pronounced with single-MPPT configurations.

Defects or degradation over time of the PV modules…inducing additional electricalmismatch losses

Any defect that produce electrical alteration of the PV curve, is adding more losses when paralleling multiple strings. This includes, for example:- Damaged or broken up cells- Faulty bypass diodes- PID effect

IR image of a ground-mount PV array

with numerous modules having bypass diodes failed in short-circuit. Heliolytics

Soliling doesn’t just cause shading but also hot spots

WHAT OTHER FACTORS SHALL BE CONSIDERED UNDER REAL WORLD CONDITIONS?

—



MPP1

MPPn

PV1

PVn

INVERTER

Up to 800Vac


INVERTER

PV1 PVn600V

Up

to

1500 V

dc

Multi-MPPT: other advantages

Bigger PV clusters may be designed

+35%Cluster size

3,7MVA 5MVA

AC-BOS cost savings (LV distribution)

400VAC 800VAC

75% lessCu/Al

Less units and resources are needed

-63%components

AC

=

===

800VAC to reduce Balance of System cost (i.e. AC side cabling) and enabling higher power units with same current (less units per power block)

More power from the same enclosure

(140kVA/130kVA) (185kVA/175kVA)

+31%

800V690V

600V480V

400V

80 175150130100

AC power vs AC voltage

= =600Vac 800Vac

Enabling cost savings with decentralized «combiner-free» PV system design

—



INVERTER

PV1 PVn600V

Up

to

1500 V

dc

Enabling cost savings with decentralized «combiner-free» PV system design

Mono-MPPT / centralized design

DC cable feeders DC Recombiner

DC Installat ion DC cable st rings

Multi-MPPT Mono-MPPT

DC-Bos

-1,4€c/ Waccost saving > 63%

100MWac system / 23 clusters x 4.4MWDC/AC Ratio = 1.15


MPP1

MPPn

PV1

PVn

INVERTER

Up to 800Vac

Multi-MPPT / decentralized design

Multi-MPPT: other advantages

—


Lowering LCOE through Opex and Energy Yield optimization

Fuseless design/ integrated diagnosis

Fuses are prone to nuisance tripping over the years. Main reasons are:• Normal aging of the components• Acceleration factors typical of PV duty: temperature & current daily cycling • PV module current ratings are rapidly increasing• Bifacial technology will likely exacerbate these issues

This increase:• O&M cost → Site inspections are needed to check and replace fuses• Energy yield losses

Idc

Multi MPPT inherently enables low cost online monitoring and fault detection of the PV array• String-level data monitoring can be embedded in the inverter for diagnostic purposes• String-level Arc fault detection can embedded in the inverter to enhance system safety• Anti PID Board

This reduce:• O&M cost → Remote diagnosis is possible avoiding Site

inspections to promptly identify the fault• Installation Cost → feature already available on the

inverter. No need to install external devices• Energy yield losses

This increase:• System availability → fast fault

detection and fast on site solution• Safety

Junction box after an Arc Fault

I-V curve with shorted bypass diodes

Mono vs. multi How many MPPT channels are good for my project?€¦ · February 19, 2020 Slide 5 MPPT –a real key inverter attribute Comparing multi-MPPT vs single MPPT (single

Documents